The present invention relates to an unloader for a silo or the like used for transferring material stored therein towards an outlet opening in the bottom thereof. The unloader comprises a pivot frame resting on the bottom of the silo and rotatable around a vertical axis, an upper protecting hood, a horizontal transport screw supported on the frame and rotating around its longitudinal axis, and driving mechanisms for pivoting said frame and for rotating said transport screw.
By means of such an unloader, chips, sawdust, bark, milled peat, or any other similar material are discharged from a silo which material, because of arching, requires an unloader covering a wide area. The transport screw rotates around its longitudinal axis and, at the same time, pivots 360 degrees back and forth. The screw transfers material in the silo from the outer periphery of the silo to its centre where the material falls down through a central opening in the bottom of the silo. The unloader can also be positioned in a storage field under a stack-like storage pile. The bottom of the silo can also have the shape of a circular sector, in which case the transport screw pivots only over the central angle of this sector.
In known unloaders of this type, the upper protecting hood of the pivot frame is, in general, fixedly connected to the pivot frame and, accordingly, rotates along with it. This results in the disadvantage that the friction between the protecting hood and the material above it causes a rather great moment resisting the rotary movement of the pivot frame. A stationary protecting hood again suffers from the disadvantage that the material to be discharged tends to form an arch in spite of the pivoting movement of the transport screw.
The object of the present invention is to provide a new unloader which eliminates both above-mentioned disadvantages.